TwoAddressInstructionPass doesn't really know how to merge live intervals when

[oota-llvm.git] / lib / CodeGen / BranchFolding.cpp

diff --git a/lib/CodeGen/BranchFolding.cpp b/lib/CodeGen/BranchFolding.cpp
index 8f519407ccd4e8c2890557861ab47989c01bf207..9dec22ec78a36de0a7fb8f3abf976815cf035a8a 100644 (file)
--- a/lib/CodeGen/BranchFolding.cpp
+++ b/lib/CodeGen/BranchFolding.cpp
@@ -264,14 +264,8 @@ static unsigned HashMachineInstr(const MachineInstr *MI) {
   return Hash;
 }
 
-/// HashEndOfMBB - Hash the last few instructions in the MBB.  For blocks
-/// with no successors, we hash two instructions, because cross-jumping
-/// only saves code when at least two instructions are removed (since a
-/// branch must be inserted).  For blocks with a successor, one of the
-/// two blocks to be tail-merged will end with a branch already, so
-/// it gains to cross-jump even for one instruction.
-static unsigned HashEndOfMBB(const MachineBasicBlock *MBB,
-                             unsigned minCommonTailLength) {
+/// HashEndOfMBB - Hash the last instruction in the MBB.
+static unsigned HashEndOfMBB(const MachineBasicBlock *MBB) {
   MachineBasicBlock::const_iterator I = MBB->end();
   if (I == MBB->begin())
     return 0;   // Empty MBB.
@@ -283,20 +277,8 @@ static unsigned HashEndOfMBB(const MachineBasicBlock *MBB,
       return 0;      // MBB empty except for debug info.
     --I;
   }
-  unsigned Hash = HashMachineInstr(I);
 
-  if (I == MBB->begin() || minCommonTailLength == 1)
-    return Hash;   // Single instr MBB.
-
-  --I;
-  while (I->isDebugValue()) {
-    if (I==MBB->begin())
-      return Hash;      // MBB with single non-debug instr.
-    --I;
-  }
-  // Hash in the second-to-last instruction.
-  Hash ^= HashMachineInstr(I) << 2;
-  return Hash;
+  return HashMachineInstr(I);
 }
 
 /// ComputeCommonTailLength - Given two machine basic blocks, compute the number
@@ -811,7 +793,7 @@ bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
   MergePotentials.clear();
   for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
     if (I->succ_empty())
-      MergePotentials.push_back(MergePotentialsElt(HashEndOfMBB(I, 2U), I));
+      MergePotentials.push_back(MergePotentialsElt(HashEndOfMBB(I), I));
   }
 
   // See if we can do any tail merging on those.
@@ -897,8 +879,7 @@ bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
               // reinsert conditional branch only, for now
               TII->InsertBranch(*PBB, (TBB == IBB) ? FBB : TBB, 0, NewCond);
           }
-          MergePotentials.push_back(MergePotentialsElt(HashEndOfMBB(PBB, 1U),
-                                                       *P));
+          MergePotentials.push_back(MergePotentialsElt(HashEndOfMBB(PBB), *P));
         }
       }
       if (MergePotentials.size() >= 2)